The present invention relates to a circuit for controlling the signals used to drive a print engine of a continuous ink jet printer and, more particularly to a circuit designed to allow for all impulses sent from the printer controller to reach the print engine, especially when the controller is requesting a print speed in excess of the printer capability.
In many common digital printing techniques, there are maximum print speeds associated with the print engine or printhead. For a continuous ink jet printer for example the maximum print speed is limited by the drop production rate. In laser printers, the maximum speed may be limited by the laser scanning speed. Even the clock rate for data transfer in the control electronics can define the maximum print speed. The print engine defined maximum speed limit will be denoted as the red line limit. To obtain maximum efficiency out of these print engines it is often desirable to operating the printers as close to the red line limit as possible. Attempting to operate the printer faster than the red line limit will lead to a printer failure. The printer failure may involve missing print, scrambled print, or even a lock up of the printer electronics.
Digital printers also often employ an encoder or tachometer to monitor the motion of the print medium relative to the printhead. The print data is transferred to the print engine in response to appropriate tachometer pulses. The existence of a maximum speed limit for the printer corresponds to there being a Printer Limited Minimum (PLM) Period between tachometer pulses below which printer failures occur.
It must be appreciated that the speed of the print media relative to the printhead typically has variation to it, in the form of wow or flutter. The period between pulses from the tachometer therefore will have some variation. When operating a digital printer near the red line limit, failure to account for such speed variations can cause the instantaneous printer speed to exceed the redline limit even if the average printer speed is less than the redline limit. That is, the tachometer pulse period may be temporarily less than the PLM period even if the average period is greater than the PLM period.
In a digital printer, even a single tachometer or encoder pulse that trails the preceding tachometer or encoder pulse by less than the PLM period can produce an error. In the prior art, this problem was dealt with in one of the following ways: 1) discarding the encoder pulse, 2) generation of an error, 3) buffering lines of data at the printhead and printing on the next available cycle, or 4) maintaining a large difference between the average speed of the transport and the maximum printing speed of the web to allow head room for peak variations in the tach. However, each of these existing approaches has drawbacks.
It would be desirable, therefore, to allow all encoder pulses to be accounted for, particularly for cases of short bursts in the encoder pulse rate due to noise and short speed variations that exceed maximum printing speed.
This need is met by the circuit according to the present invention wherein incoming encoder pulses are processed to guarantee a minimum pulse width and maintain a higher average throughput for a print engine.
In accordance with one aspect of the present invention, a circuit for processing incoming encoder pulses for an imaging system, comprises an incoming signal from the controller, and means for processing the incoming signal by effectively creating an edge transition at the incoming frequency of the control signal. All the information from the controller is processed, and pulses are not lost or discarded.
Objects and advantages of the invention will be apparent from the following description, the accompanying drawing and the appended claims.